The curing of back pain is one of the most important objectives of neurosurgeons, orthopedists, anesthesiologists and neurologists. Back pain is one of the most common forms of pain and accounts for huge amounts of disability and loss of labor throughout the world. The curing of back pain heretofore has been in the domain of surgery, percutaneous injection of chemicals into the intervertebral disc, percutaneous removal by mechanical means of intervertebral discs, RF heating of peripheral nerves outside of the intervertebral disc to interrupt nerve fibers outside of the disc, and various forms of drug and rehabilitation therapy. Nowhere in the literature of prior art or clinical experience has there been any report or knowledge of placing a probe into the disc for the purpose of heating the entire disc, nor has there been any indication that the heating of a disc to be a safe and effective method of alleviating intractable back pain due to pathology of the disc itself or interrupting of various neural processes in and around the disc. It is the objective and novelty of the present invention that the introduction of a probe or other element into the disc for the purpose of heating the disc provides substantial pain relief in a way which has not been anticipated heretofore.
The use of radiofrequency (RF) electrodes and power sources for generators is common in the field of neurosurgery, anesthesiology, and cardiology for the destruction of neural tissue. This is typified by the RF electrodes and RF lesion generator systems of Radionics, Inc. in Burlington, Mass. Heretofore, the lesion electrodes are placed at the target site under various types of guidance, including stimulation, x-ray control, tomographic image control, and stereotactic apparatus. The electrode typically consists of an insulated shaft with an exposed tip which is elevated to radiofrequency potential. A second electrode, usually a dispersive electrode with a large area, is placed elsewhere on the body to return the radiofrequency current, thereby making the patient's body part of the radiofrequency circuit. The intensity of radiofrequency current at the exposed tip of the radiofrequency lesion electrode causes the heating of the tissue in the neighborhood of the electrode, and thus the destruction of that tissue. Until now, the tissue has always been either direct neurological tissue, such as in the brain or the spinal cord, or muscle tissue, as in the heart in the case of cardiac ablation. A typical example of radiofrequency lesion making is for the relief of various types of back pain, as in the case of facet denervation or in direct destruction of low back nerve structures such as the sympathetic nerves or communicating rami. In the case of facet denervation, the electrode is placed near a small nerve branch which innervates the spinal facet joints, and a heat lesion is made interrupting the noxious signals emanating from these joints. RF heating is also used for destruction of ganglia such as the sphenopalatine ganglion or of other nerves which are ramifiications of the nerves which exit from the spinal column. The mechanism is a direct interruption of nerves and thus of the pain signals from the affected areas to the spinal cord. These procedures have been effective, however, there are many pain syndromes which relate to the region around the intervertebral disc itself. It is very difficult to achieve a comprehensive destruction of the nerves which innervate the disc. This is because the disc is innervated by multiple nerve branches. Some of these branches, notably those which innervate the clinically important posterior part of the disc, lie close to the exiting spinal nerves. Destruction of these branches with a heat lesion would therefore carry the risk of damaging the spinal nerves. It would be a very effective treatment for so-called discogenic back pain to be able to simply and with a minimal number of percutaneous needle sticks denervate or destroy the numerous nerve structures which are present at the surface of the entire disc, without endangering the important nerve structures inside and exiting from the spinal canal.
It has been a characteristic of RF lesion making in the nervous tissue or in the soft muscle tissue that the RF electrode, which affects the heating, be placed in proximity to the tissue to be destroyed. That is, by various stereotactic means, X-ray, fluoroscopy, CT or MR guidance, or stimulation and recording, the tip of the RF electrode is placed directly on or very near the target nerves themselves, and the heating is subsequently carried out. A technique which has heretofore not been done is to place the electrode in a position relatively remote from the nerves to be destroyed, heat an intermediate structure which then carries over to more remote neural structures, and thereby destroy those remote neural structures. That methodology and approach is one of the novel and interesting aspects of the present invention.
Several methods exist which have sought to reduce back pain emanating from the intervertebral disc by removing percutaneously tissue from the disc. The most popular of these methods is the so-called percutaneous discectomy procedure developed by Dr. Gary Onik. In this procedure, a special needle is placed into the intervertebral disc by a puncture through the skin on the back of the patient under fluoroscopic guidance. Once the needle is in place, a mechanism within the needle draws in the intervertebral disc material by a vacuum, cuts it off, and sucks it out by means of a reciprocating cutting element within the needle itself. This effectively reduces the volume within the disc and, if a disc is bulging or otherwise enlarged, the loss of volume will tend to reduce the impingement of the surface of the disc on macroscopic nearby nerves. It will not be effective at destroying the numerous nerves around the periphery of the disc if they are the cause of the discogenic pain.
The present invention relates to a new and novel technique of introducing an RF electrode or other heating electrode into the intervertebral disc, typically under fluoroscopic control, and heating the entire disc to a temperature significantly above body temperature. The heated disc will, in turn, heat the nerves which innervate its surface, and they will be destroyed or altered if the heat of the disc is elevated to an appropriately high temperature.
The prior art of radio frequency lesion generation deals with RF electrodes being placed into tissue such as the brain tissue or muscle tissue, in which the nerve cells to be destroyed actually reside adjacent to the electrode. That is, the tip of the electrode with the active exposed surface, is placed in the vicinity of the nerves, if not in the neural tissue itself. Thus, by applying the radio frequency current, the tissue in the immediate vicinity of the electrode tip is heated and the nerve fibers to be destroyed are thereby killed. This is typically used in the brain for curing of various neurological disorders, such as thalamotomies, and it is also used in other parts of the body, such as in the neck or back region to cure various forms of spinal pain related to disorders of the spinal facets or disorders related to various ramifications of nerves emanating from the spinal column. A background to this technique, which is well known in the prior art, is described in the papers of Cosman and Cosman.sup.1, Cosman, Nashold et al..sup.2, and M. Sluijter.sup.3,4,6. The concept of a direct neurological lesion being made by RF heating is well known in medical practice and has been utilized for decades.
As alluded to above, one of the outstanding problems in the treatment of back pain relates to neural structures that innervate the intervertebral disc itself. There are numerous sensory nerves which cluster at the exterior surface of the intervertebral disc and sense mechanical deformations of the disc. These nerves have evolved most probably as a protection mechanism against excessive stress of the disc wall, which in turn may cause serious damage to the disc, such as rupture, bulging, or herniation. In the situation of an overstressed disc, a rupture can cause extrusion or bulging of the inner material of the disc beyond the external wall with consequent pressure on nerves in the vicinity. This is one of the most common forms of back pain, and usually must be cured by surgery or percutaneous disc removal. However, another very common form of back pain related to the disc is the mere irritation or stimulation of the numerous small nerves that innervate the periphery of the disc and sense its mechanical stress. These nerves are found ubiquitously over the surface of the disc. In the situation where herniation or extrusion of the disc has not taken place, yet these numerous tiny nerves are stimulated to produce a painful response, there is no simple surgical treatment, and the patient may be in extreme pain and distress as a result. It may be fruitless to attempt to place an RF electrode directly on these small nerves, as they are distributed over an extensive surface of the disc, making it impractical and dangerous to introduce a sufficient number of electrodes in to denervate all of them. More particularly, it is not possible to know beforehand exactly which of these sensing nerves is causing the problem. Indeed, there may be a large number of them over the entire surface of the disc in the situation that the disc is extremely distorted, or alternatively only a subset of them at one particular location for a more focal disc bulge.
Therefore there exists a need for heating and desensitizing these nerves around the disc by minimal invasion to the body, while at the same time sparing the larger nerve bundles running in the vicinity of the disc. Such a technique would produce significant pain relief in a substantial fraction of patients suffering from back pain. This then is one of the objectives of the present invention.
Another objective of the present invention is a technique for heating and destroying neural structures via an intermediate anatomical body such as bone, cartilage, or in the case of the present invention, the intervertebral disc. Thus the present invention relates to what might be described as an indirect radiofrequency lesion method whereby the destruction of desired neural structures is done not by direct placement of an RF electrode near the structures, but rather by the radiofrequency heating of an intermediate structure, which in turn diffuses the heat to the neural structures in a more diffuse and global fashion. An objective of the present invention is to produce this indirect or global heating of an intervertebral disc so as to relieve diffuse back pain related to innervation of the disc's surface itself. This is a new and unique technique with a new and unique clinical indication for relief of pain which heretofore has been refractory to surgical or percutaneous methods.
Associated with indirect or global radiofrequency heating technique, it is important to be able to monitor temperature, not only at the direct point of RF electrode heating, but also at remote points in space so as to monitor and control the exact temperature distribution. Thus it is another objective of the present invention to provide electrode and temperature monitoring systems to carry out the direct and/or indirect monitoring of points in space relative to the primary RF lesion electrode for safer and more effective control of the heating process.